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Hiss bundle branch blockade: causes, symptoms, diagnosis, treatment
Medical expert of the article
Last reviewed: 07.07.2025
Bundle branch block is a partial or complete disruption of impulse conduction along a branch of the bundle; bundle branch block is a similar cessation of conduction along the entire bundle branch of the bundle of His. Both disorders are often combined. This usually does not lead to the development of clinical manifestations, but the presence of any of these disorders indicates heart damage. The diagnosis is established based on ECG data. No special treatment is required.
Conduction block can be the result of various heart diseases, including organic pathology of the organ without any other heart pathology.
Right bundle branch block may occur in apparently healthy individuals. It may also occur in anterior myocardial infarction, reflecting severe myocardial damage. Newly developed right bundle branch block is an indication for examination for heart pathology, but often nothing is found. Transient right bundle branch block may occur in pulmonary embolism. Despite the fact that right bundle branch block disrupts the shape of the ventricular complex, it does not cause significant difficulties in ECG diagnostics of myocardial infarction.
Left bundle branch block is associated with structural heart disease more often than right bundle branch block. Left bundle branch block usually precludes the use of an ECG to diagnose myocardial infarction.
Bundle branch block involves the anterior and posterior branches of the left bundle branch. Interruption of conduction along the anterior branch of the left bundle branch is characterized by moderate prolongation of the QRS complex (< 120 ms) and a negative deviation of the QRS axis angle of more than -30° (left axis deviation). Posterior branch block of the left bundle branch is characterized by a positive deviation of the angle of more than +120°. The association of bundle branch block with structural pathology is the same as that of left bundle branch block.
Incomplete block may be associated with other conduction disturbances: Right bundle branch block and left anterior or posterior fascicle block (bifascicular block); anterior or posterior fascicle block, right bundle branch block, and first-degree AV block (incorrectly called trifascicular block; first-degree AV block usually has a cause at the level of the AV node). Trifascicular block involves the combination of right bundle branch block with alternating transient left anterior and posterior fascicle block or alternating left bundle branch block and right bundle branch block. The presence of bifascicular or trifascicular block after myocardial infarction reflects extensive myocardial damage. Bifascicular block does not require specific treatment until second- or third-degree AV block occurs. True trifascicular block is an indication for immediate and then permanent cardiac pacing.
If the complex is prolonged (more than 120 ms), but does not have a shape characteristic of the right bundle branch block or the left bundle branch block, nonspecific intraventricular conduction block is diagnosed. Conduction disturbances may occur at the level of the Purkinje fibers and be a consequence of slow conduction from myocyte to myocyte. Specific treatment is not prescribed.
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